var mask = (function () {
	var ele = document.createElement("div"),
		body = document.getElementById('grad');

	function addMask () {
		ele.innerHTML = "放开那鼠标";
		ele.className = "mask";
		body.appendChild(ele);
	}

	function removeMask () {
		try {
			body.removeChild(ele);
		} catch(e) {
			console.log('这个元素已经被删除过了，不能再删除这个元素了');
		}
	}

	return {
		addMask: addMask,
		removeMask: removeMask
	}
}());
